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How Being Right or Left Handed Can Affect Depression Treatment

May 8, 2012
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The way we use our hands may be an indicator of how emotions are organized in our brains. This has significant implications for "motivation," the drive to approach or withdraw from physical and social stimuli. Motivation is a basic building block of human emotion.

Scientists have believed that “approach” motivation is computed in the left hemisphere of the brain. They also believe that “withdraw” motivation is in the right hemisphere. Geoffrey Brookshire and Daniel Casasanto of The New School for Social Research challenged this idea with their study. What they found is that while that might be true for right-handers, the opposite is true for left-handers. They used EEG to compare brain activity.

This isn’t true for all brain activity. Most cognitive functions stay put: language is on the left hemisphere for everybody. The switch for types of motivation was unexpected and appears to be novel. Still Casasanto says it was entirely unpredictable.

“We predicted this hemispheric reversal because we observed that people tend to use different hands to perform approach- and avoidance-related actions,” says Casasanto. People use their dominant hand for actions to approach or avoid.

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“Approach motivation is computed by the hemisphere that controls the right hand in right-handers, and by the hemisphere that controls the left hand in left-handers,” says Casasanto. “We don’t think this is a coincidence. Neural circuits for motivation may be functionally related to circuits that control hand actions – emotion may be built upon neural circuits for action, in evolutionary or developmental time.”

In treating depression, stimulation is used to increase neural activity in the left hemisphere. “Given what we show here, this treatment may be detrimental to left-handers.”